Work around crash when display is removed.

After a display is removed, there may be a brief time
when a Context still exists that is bound to it.
We need to provide metrics in this case.

Bug: 7131637
Change-Id: I11b264a000653adbf0f3da399eaab66c4b40fb2a

Author: Jeff Brown

core/java/android/app/ActivityThread.java

@@ -1586,7 +1586,15 @@ DisplayMetrics getDisplayMetricsLocked(int displayId, CompatibilityInfo ci) {
         CompatibilityInfoHolder cih = new CompatibilityInfoHolder();
         cih.set(ci);
         Display d = displayManager.getCompatibleDisplay(displayId, cih);
-        d.getMetrics(dm);
+        if (d != null) {
+            d.getMetrics(dm);
+        } else {
+            // Display no longer exists
+            // FIXME: This would not be a problem if we kept the Display object around
+            // instead of using the raw display id everywhere.  The Display object caches
+            // its information even after the display has been removed.
+            dm.setToDefaults();
+        }
         //Slog.i("foo", "New metrics: w=" + metrics.widthPixels + " h="
         //        + metrics.heightPixels + " den=" + metrics.density
         //        + " xdpi=" + metrics.xdpi + " ydpi=" + metrics.ydpi);